[PATCH] ppc64: fix signal handler arguments

This is the first of 3 patches from David Woodhouse which fix various
problems with signal handling on ppc64.  (This is David's patch plus a
couple of comment fixes from me.)

Without this patch, a signal handler that is called as a result of delivery
of a signal while a process is waiting in sigsuspend() will have wrong
values given to it for the second and third arguments.  The reason is that
we were returning to userspace via the syscall return path, which doesn't
bother to restore r4 and r5.  This patch arranges for the return to
userspace to be done via ret_from_except in this case, which restores all
registers.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ppc64/kernel/entry.S

@@ -265,16 +265,21 @@ _GLOBAL(save_nvgprs)
 _GLOBAL(ppc32_sigsuspend)
 	bl	.save_nvgprs
 	bl	.sys32_sigsuspend
-	b	syscall_exit
+	b	70f
 
 _GLOBAL(ppc64_rt_sigsuspend)
 	bl	.save_nvgprs
 	bl	.sys_rt_sigsuspend
-	b	syscall_exit
+	b	70f
 
 _GLOBAL(ppc32_rt_sigsuspend)
 	bl	.save_nvgprs
 	bl	.sys32_rt_sigsuspend
+	/* If sigsuspend() returns zero, we are going into a signal handler */
+70:	cmpdi	0,r3,0
+	beq	.ret_from_except
+	/* If it returned -EINTR, we need to return via syscall_exit to set
+	   the SO bit in cr0 and potentially stop for ptrace. */
 	b	syscall_exit
 
 _GLOBAL(ppc_fork)

arch/ppc64/kernel/signal.c

@@ -98,7 +98,7 @@ long sys_rt_sigsuspend(sigset_t __user *unewset, size_t sigsetsize, int p3, int
 		current->state = TASK_INTERRUPTIBLE;
 		schedule();
 		if (do_signal(&saveset, regs))
-			return regs->gpr[3];
+			return 0;
 	}
 }
 

arch/ppc64/kernel/signal32.c

@@ -284,14 +284,12 @@ long sys32_sigsuspend(old_sigset_t mask, int p2, int p3, int p4, int p6, int p7,
 		schedule();
 		if (do_signal32(&saveset, regs))
 			/*
-			 * If a signal handler needs to be called,
-			 * do_signal32() has set R3 to the signal number (the
-			 * first argument of the signal handler), so don't
-			 * overwrite that with EINTR !
-			 * In the other cases, do_signal32() doesn't touch 
-			 * R3, so it's still set to -EINTR (see above).
-			 */
-			return regs->gpr[3];
+			 * Returning 0 means we return to userspace via
+			 * ret_from_except and thus restore all user
+			 * registers from *regs.  This is what we need
+			 * to do when a signal has been delivered.
+			 */
+			return 0;
 	}
 }
 
@@ -587,14 +585,12 @@ int sys32_rt_sigsuspend(compat_sigset_t __user * unewset, size_t sigsetsize, int
 		schedule();
 		if (do_signal32(&saveset, regs))
 			/*
-			 * If a signal handler needs to be called,
-			 * do_signal32() has set R3 to the signal number (the
-			 * first argument of the signal handler), so don't
-			 * overwrite that with EINTR !
-			 * In the other cases, do_signal32() doesn't touch 
-			 * R3, so it's still set to -EINTR (see above).
-			 */
-			return regs->gpr[3];
+			 * Returning 0 means we return to userspace via
+			 * ret_from_except and thus restore all user
+			 * registers from *regs.  This is what we need
+			 * to do when a signal has been delivered.
+			 */
+			return 0;
 	}
 }